The novel polyorganosiloxane material S-101 modified with amino and hydroxy groups is synthesized. Shade darkening effect of modified polyorganosiloxane on dyed polyester microfiber fabric is investigated by reflectance spectrum, color yield (K/S), and the color differences (Delta E). The colorimetric data of CIELAB is discussed. The results show that the novel material of silicone polymer modified with amino and hydroxy groups has excellent shade darkening effect on dyed polyester microfiber fabric. The rates of the color yield increase (I%) of all dyed fabric with four dyes (Disperse Yellow S-4RL, Red GS, Blue 2BLN, and Black SF-R) exceed 10%. The shapes of the reflectance spectra curves of the dyed fabrics before and after treated with S-101 are not noticeable change. The dyed fabrics with the polymer have not significant effect on the wash fastness and wet rubbing fastness. The low reflectance thin film on dyed fabrics is formed. (C) 2007 Wiley Periodicals, Inc.